You should always make sure your opponent leaves the game with as little points as possible, that is the point of this whole 'competition' thing called the SuperXV. That alone, is a good enough reason to take the points off ANY team. But still...
If the Reds or Tahs do something stupid, maybe half their team tests positive to drugs, or they get found to have played half a game with 16 on the field. I'm pretty sure Sanzar can take points off them if they please, therefore even though the Brumbies are not in line for a finals spot, there is always a slight possibility of the Brumbies somehow making it.
Personally i would kick it out. But the point is, what everyone here considers the 'morally right thing' to do is completely subjective. Therefore if you give away a penalty in your own half after the siren, you can't rely on the opposition to go with whatever decision you personally consider morally acceptable. The point is, the opposition's moral values are completely out of your control, everyone should be aware of this and can only blame themselves if they get into a situation like tonight.